Method of purifying gases containing combustible gaseous or vaporous impurities

ABSTRACT

Method and apparatus for purifying an air or gas flow of combustible vaporous or gaseous impurities by passing the air or gas through an adsorption filter and charging the filter to a predetermined level. After the filter is so charged, the air or gas flow is interrupted and the filter is desorbed by passing a heated inert gas generated by stoichiometric burning of hydrocarbons through the filter.

Waited States Patent [191 Winter METHOD OF PURIFYING GASES CONTAINING COMBUSTIBLE GASEOUS OR VAPOROUS IMPURITIES [75] Inventor: Karl Winter, Dortmund, Germany [73] Assignee: CEAG Concordia Elekrizitats Aktiengesellschatt, Dortmund, Germany [22] Filed: June 15, 1971 [21] Appl. No.: 153,345

[30] Foreign Application Priority Data June 19, 1970 Germany 2030153 [52] US. Cl. 423/210, 23/277 C [51] Int. Cl Bold 53/34 [58] Field of Search 23/277 C; 423/210, 215,

[4 1 Dec. 10, 1974 [56] References Cited UNITED STATES PATENTS 3,395,972 8/1968 l-lardison 423/210 Primary ExaminerEarl C. Thomas I Attorney, Agent, or Firm-Herbert L. Lerner 5 7] ABSTRACT Method and apparatus for purifying an air or' gas flow of combustible vaporous or gaseous impurities by passing the air or gas through an adsorption filter and charging the filter to a predetermined level. After the filter is so charged, the air or gas flow is interrupted and the filter is desorbed by passing a'heated inert gas generated by stoichiometric burning of hydrocarbons through the filter.

3 Claims, 1 Drawing Figure METHOD OF EURIFYING GASES CONTAINING COMBUSTIBLE GASEOUS OR VAPOROUS IMPURITIES My invention relates to the minimization of pollutants in the air, and, more particularly to a method and apparatus for purifying an air or gas flow of combustible vaporous or gaseous impurities or pollutants by means of adsorption filters.

Methods and apparatus are available for purifying the air or other carrier gases calm areas, which are mostly are very difficult to operate or require an unjustifiable expense to remove or to destroy harmful gaseous or vaporous substances. Initially, it was attempted to dispose of these substances, which are emitted in large quantities, for instance, due to incomplete burning processes, by their rarefaction with atmosphere. Also, for instance, the expulsion of the impurities from stationary plants into higher air layers has been attempted. However, no fundamental solution of the problem was achieved, since a heavy rarefaction with the atmosphere or an expulsion into the higher air layers is acceptable in remote and windy areas, but not in densely populated, and where such air pollutants are created in huge quantities.

in order to control the most harmful portions of exhaust gases, as long as these pollutants are combustible gases and vapors, previously it was attempted either to separate them from the carrier gas by adsorption filters, such as, activated charcoal, or to pass them through an after-bumer and to change them into harmless substances therein. For example, in the ideal case, pure hydrocarbons are burned and changed without residue into carbon dioxide and water. In this method, itwas also attempted to lower the burning temperatures by utilization of catalysts. However, both of these methods have not resulted in achieving the desired aim, as in both cases, the disposal of the polluting gases or vapors is possible only with an enormous expense. The utilization of activated charcoal filters alone, for instance, is considered to be economically justifiable only if the concentration of the impurities does not exceed 5 milligrams per standard cubic meter, as the filtering substance is consumed too rapidly if the concentration of pollutants or impurities is higher. An afterbuming of the combustible air pollutants in catalysts is economical only if the concentration of the above mentioned pollutants is not less than 100 milligrams per standard cubic meter of air. For the heating of all substances used in the burning process to the required temperature of reaction, the concentration is even substantially higher.

However, in order to prevent unburned gaseous particles reaching the purified air side if the gaseous mixture temperatures are too low, an additional heating of the gas mixture follows to support the combustion process. Therefore, the exhaust gas heat was attempted to be used for the burning process in the heat exchanger, and for supplemental heat, an additional heating apparatus is available. However, such devices become so expensive, that the disposal of these mostly harmful or illsmelling air pollutants in the present catalytic afterburning devices is not worthwhile if the concentration is lower than 100 milligrams per cubic meter. Consequently, a satisfactory solution at present is not available for the removal of the combustible air pollutants from the air having a concentration range of between 5 and 100 milligrams per standard cubic meter.

In order to remedy this problem, there has already been devised a process for purifying an air or gas flow of combustible vaporous or gaseous impurities by means of adsorption filters, wherein the air or gas flow is purified by means of an adsorption filter after being charged with a predetermined amount of combustible impurities. The filter is desorbed by a heated air flow in counterflow, the desorbate is burned in a catalytic afterburner, and a portion of the mixture of air and burned desorbate is repeatedly passed through the filter until the filter charge decreases to a level where the filter can again be used for purifying the air or gas flow. However, so-called catalyst poisons are created in this process, for instance, organic phosphorous compounds, and the device slowly becomes ineffective.

There is also already known a process, in which the gases are retained in the adsorption filter until the filter reaches its saturation level, then the adsorption filter is heated and the gases expelled therefrom and burned in a burning device or in the heated catalyst layer. Subsequently, the heat supply to the adsorption filter and to the burner or the catalyst layer is discontinued and the adsorption process is restarted. This method uses a concurrent flow, so that the harmful gas particles pass from the polluted air side to the purified air side of the repeatedly used activated charcoal filter and are not completely desorbed because the heated air flow is subject to cooling along its path of travel through the filter. As already known, the heating temperature has an upper limit of approximately 400 C because of the inflammability of the activated charcoal, which cannot be exposed to the influence of the oxygen present in the heated air at this temperature. Moreover, this process is inefficient because the entire air flow has to be heated, not only the necessary portion thereof.

An object of my invention is to provide a method and apparatus for purifying an air or gas flow of combustible vaporous or gaseous impurities by means of adsorption filters, which eliminate the above drawbacks.

Another object of my invention is to provide such a method and apparatus which is efficient and economical.

Yet another object of my invention is to provide such a method and apparatus which lends itself to being easily automated.

Other objects, advantages and features of this invention will become more apparent from the following description.

These objects are achieved according to the principles of my invention in that the air or gas flow is purified by an adsorption filter, and after the charge of the filter with combustible impurities has reached a predetermined level, it is desorbed in counterflow by a hot inert gas generated by stoichiometric burning of hydrocarbons, and then the desorbate, carried away by the inert gas, is subsequently burned with an additional supply of air or oxygen. This method is utilized to advantage when the adsorption filter is saturated with impurities. Preferably, activated charcoal is used as the adsorption material, but also silica gel for adsorption of moisture and zeolites could also be used.

The invention will be further described with reference to embodiments thereof, illustrated by way of example on the accompanying drawing which is a diagrammatic view of an embodiment of my invention for purifying the gas flow of impurities or pollutants.

The illustrated apparatus comprises two burning chambers 4 and 5. The first burning chamber 4 is connected via .a closing member 41 to a gas discharge outlet 3 on the purified air side and the second burning chamber 5 is connected via another closing member 51 to the gas supply inlet 2 on the polluted air side of the adsorption zone or filter 1. The gas inlet and outlet can be closed by similar closing members 21 and 31.

When the apparatus commences operation, only closing members 21 and 31 of the inlet 2 and the outlet 3 are open, so that the air or gas flow to be treated passes through the adsorption filter 1, which adsorbs the gaseous or vaporous impurities. Closing members 51 and 41, which are located behind the closing member 21 and before the closing member 31, respectively, in the direction of gas flow, are closed.

When the filter is charged by the impurities to a predetermined level, such as the saturation limit of the adsorption material with combustible impurities, the dos ing members 21 and 31 are closed and the closing members 41 and 51 are opened. An inert gas, generated in the first burning chamber 4 by stoichiometric burning of hydrocarbons and heated to a predetermined termperature, passes through the open closing member 41 and desorbs the adsorption filter 1 in counterflow. Subsequently, the inert gas enriched with the desorbate flows through the closing member 51 in the second burning chamber 5. An air or oxygen surplus is added to this mixture of inert gas and vaporous desorbate is produced in this burning chamber 5. The air or oxygen surplus is chosen so as to enable a complete burning of the desorbate.

The inert gas serving as carrying gas may be generated, for instance without excess air by burning oil or propane gas. For example, approximately 400 m /h of inert gas are necessary to desorb 100 kg of vaporous impurities, stored in approximately 1 cubic meter of activated charcoal after purifying an air flow of approximately 10,000 m /h having a harmful gases content of approximately 500 mgl m. The inert gas is heated to a temperature of approximately 500C after the moisturizing cooling, and is subsequently supplied to the buming devices.

After the adsorption filter is ready to resume its purifying function by utilization of the method according to the invention, the closing members 41 and 51 are closed and the gas to be cleaned is again subjected to a purification process by opening the closing members 21 and 31 so that the gas passed through the adsorption filter l.

The present invention may be used for removing combustible, annoying or harmful vaporous of gaseous pollutants of the air or other gases. The concentration of these annoying or harmful impurities in their carrier gases is of a secondary importance influencing only the time required for desorbing to be completed. If a plu rality of adsorption filters is used, it is possible to switch the gas flow to be treated from a saturated to a regeneratedadsorption filter, and, consequently, a simultaneous adsorption of the impurities of the gas flow and a desorption of a filter previously charged with separated and adsorbed impurities can be conducted. The device according to the invention can also be automated, so that it does not need human control, if all the closing members are provided with a conventional remote control device, and the concentration and quan tity of supplied air are continuously measured.

It will thus be seen that the objects set forth above,

among those made apparent from the preceding description, are efficiently attained and, since certain changes may be made in the above apparatus and method without departing from the scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

I claim:

1. A method of purifying an air or gas flow of combustible vaporous or gaseous impurities comprising the steps of passing the air or gas through an adsorption zone in one direction thereof to purify said air or gas, charging said zone to a predetermined level, generating a hot inert gas by stoichiometrically burning a hydrocarbon, passing said hot inert gas through said zone in a direction opposite to that of said air or gas flow to desorb the adsorbed combustible gaseous or vaporous impurities from said zone, thereby producing a mixture of a desorbate and said inert gas, and adding to said mixture sufficient oxygen to enable complete burning of the desorbate and completely burning said desorbate in said mixture.

2. A method as set forth in claim 1 wherein said adsorption zone comprises a filter.

3. A method as set forth in claim 2, wherein said filter comprises activated charcoal, silica gel or zeolite. 

1. A METHOD OF PURIFYING AN AIR OR GAS FLOW OF COMBUSTIBLE VAPOROUS OR GASEOUS IMPURITIES COMPRISING THE STEPS OF PASSING THE AIR OR GAS THROUGH AN ADSORPTION ZONE IN ONE DIRECTION THEREOF TO PURIFY SAID AIR OR GAS, CHARGING SAID ZONE TO A PREDETERMINED LEVEL, GENERATING A HOT INERT GAS BY STOICHIOMETRICALLY BURNING A HYDROCARBON, PASSING SAID HOT INERT GAS THROUGH SAID ZONE IN A DIRECTION OPPOSITE TO THAT OF SAID AIR GAS FLOW TO DESORB THE ADSORBED COMBUSTIBLE GASEOUS OR VAPOROUS IMPURITIES FROM SAID ZONE, THEREBY PRODUCING A MIXTURE OF A DESORBATE AND SAID INERT GAS, AND ADDING TO SAID MIXTURE SUFFICIENT
 2. A method as set forth in claim 1 wherein said adsorption zone comprises a filter.
 3. A method as set forth in claim 2, wherein said filter comprises activated charcoal, silica gel or zeolite. 